The present invention relates to a method according to the preamble of the claim and to a machine tool suitable for implementing the method.
Laser stock machining has become established in a great many industrial manufacturing processes; using lasers it is possible to machine three-dimensional structures from virtually any material. By means of suitable laser sources, beam guides and optical devices, in conjunction with numerical controls, the workpieces can in many cases be finish-machined to the desired tolerance. However, in precision mechanics, more particularly precision engineering and micro-technology, there are ranges of application in which the accuracy and surface quality of the laser machining is insufficient and either finishing is necessary by means of conventionally operating machine tools, or the latter are used from the outset.
Performing laser operations on workpieces set up on other machines has also been repeatedly attempted in practice using robot-like devices, which has led to substantial and mostly intolerable inaccuracies and has required appropriate further finishing operations.
A method according to the preamble of claim 1 may be inferred from JP-A-61164738, according to which a laser source is arranged on a conventional CNC machining centre. By means of a vertical tool store in which a laser machining head is also stored along with cutting tools, cutting tools and optionally also the laser machining head with its cone on the spindle side are inserted by way of a tool-changing device into the bore of the main spindle of the machine. The laser machining head features mirrors which, because of the laser source flange-mounted on the headstock, guide a laser beam into the machining direction via a horizontal beam guide tube.
The drawback with this machining centre is the direct arrangement of the vibration-sensitive laser source on the headstock and the limitation to smaller outputs also associated with it for reasons of weight and space. The rough cutting operation and the conventional tool-changing device which causes sudden loads make precise finishing operations impossible and require fresh adjustment of the laser before every use of the said laser. Moreover, the open design of the beam guide is extremely susceptible to contamination, so that even just rough laser machining operations can only be performed with difficulty.
Another numerically controlled machine tool for two- or three-dimensional machining operations to which a laser source is connected is known from US-A-5160824. The laser beam, in the case of a laser machining operation, is guided through the hollow spindle of the machine tool and there emerges via an optical system and allows, in particular, the finishing of deep-hole bores. The optical system is provided with a clamping device which is compatible with those for cutting tools and when they are being used it is held, for example, by means of a tool-changing device.
The laser machining is thus limited to machine tools of which the main spindle has a hollow shaft and is designed in conjunction with high frequency motors above all for high-speed machining operations.
The object of the present invention is therefore to provide a method and a machine tool which extend the range of application of laser stock machining in an efficient manner and enhance the quality, more particularly the machining accuracy achievable on the workpiece. The overall accuracy of the system should be influenced solely by the particular machining method selected and not by a system change.
The subject of the invention is characterised by its ability to be particularly easily integrated into existing manufacturing processes.
The term inoperative/park position used in the claim refers to a position within the machine tool in which the laser device does not interfere with the cutting operation or the cutting operation cannot damage the laser machining head. The inoperative position and the park position may be identical; however, two different positions may be provided in order to shorten the set-up times, the inoperative position describing a pivoted-away position of the laser machining head which does not interfere with the next cutting operation. xe2x80x94Accordingly, the park position is defined as the position which does not affect cutting operations neither endangers the laser machining head.
Unlike the known arrangements in which a laser beam is guided to a dedicated laser machining centre, the subject of the invention allows all the original functions of a machine tool to continue to be used unreservedly, i.e. the cutting centre is extended by the addition of a further machining method without any cutbacks or losses of quality.
The coordination according to the invention of the laser source with a machine tool or machining centre can be achieved most easily by means of a flexible beam arm, known per se (K. H. Arnold GmbH and Co, D-882214 Ravensburg), with a constant beam path length; this requires only a few changes to be made to the machine tool or the addition to the numerical control program of an additional tool with appropriate parameters. The laser machining head is accommodated in the same tool holder as previous or subsequent operations, so that no stochastic errors are produced. Moreover, the inherent systematic error can be corrected, as a result of which only minimal stock allowances are required for the operations that follow. xe2x80x94It is thus only the machining method, and not the change from laser stock machining to cutting or vice versa, that affects the overall accuracy of the system.
The position accuracy of the laser beam is predetermined by the accuracy of the machine tool; the surface roughness of the resulting laser stock machining, on the other hand, is determined by the laser system used and by the material properties of the workpiece. In each case the dimensional accuracy and quality of the machining can be improved over that of laser machining by the subsequent use of cutting tools.
The emissions arising in the course of laser machining are within the range of that of cutting, so that, apart from glare protection, no other safety precautions on the machine tool are necessary.
The swivelling away of the laser machining head, after its use, enables the machine tool to be handled in the usual manner and prevents the said laser machining head from being damaged.
The beam guide is space saving and permits very easy tool changeover.
The zero correction allows statistical errors to be eliminated and stock allowances to be minimized in subsequent precision cutting operations.
A rigid design of the laser machining head produces the maximum axial and angular accuracy, it thus increases the accuracy of the machining and saves additional adjustment operations, so that only the usual necessary focusing of the beam is required.
In the case of a lateral beam supply, embodiments are expedient in which joints with conventional cooled metal mirrors are incorporated.
A direct mechanical connection of the laser machining head to the beam supply is space saving and economical.
A clamping device present on the laser machining head permits tool changeover, in the same way as is usual with the cutting tools.
A clamping device with a centring cone is particularly advantageous with respect to ease of handling and accuracy.
Incorporating a hollow shaft in the machine tool enables the laser beam to be guided particularly easily to the machining head.